This invention relates to modulation systems and methods, and more particularly to integrated circuit modulators.
Baseband quadrature modulators are widely used in radio frequency (RF) communication systems, including but not limited to wireless communications terminals such as mobile radiotelephones. As is well known to those having skill in the art, a baseband quadrature modulator modulates an input signal to produce in-phase (I) and quadrature (Q) baseband modulated outputs. The qaudrature modulator often is referred to as an I/Q modulator. The in-phase and quadrature baseband modulated outputs generally are provided to an RF modulator that modulates the I and Q modulated inputs onto a carrier frequency for transmission by an antenna.
Baseband I/Q modulators may be provided in an integrated circuit, to provide an integrated circuit transmit module. For example, an Application Specific Integrated Circuit (ASIC) may include a baseband I/Q modulator and supporting circuitry, such as an interface to a Digital Signal Processor (DSP) and/or an interface to a controller or Central Processing Unit (CPU). See for example, the data sheet for the Philips PCF50732 Baseband and Audio Interface for GSM, May 3, 1999. Other baseband modulator integrated circuits are well known to those having skill in the art, and need not be described in further detail herein.
Integrated circuit baseband modulators generally are tested by applying functional and/or manufacturing test vectors to the integrated circuit baseband I/Q modulator. Input and output samples then can be compared using an external test bench, by comparing the signals to one another or to a known golden sample.
Unfortunately, these testing procedures may be time consuming and/or costly. Moreover, although the test vectors may allow testing of the integrated circuit during production, it may not provide a solution for continued testing of the integrated circuit. For example, when the integrated circuit is used in a mobile radiotelephone, problems may arise with the integrated circuit baseband I/Q modulator after manufacturing, that may remain undetected in the field. In particular, the integrated circuit baseband I/Q modulator may be subject to input data and/or programmed with DC offsets that are outside the linear operating range of a Digital-to-Analog Converter (DAC) that is contained within the baseband I/Q modulator. This may provide erroneous modulated data, even though the modulator appears to be working properly. Accordingly, these problems may be difficult to detect and resolve after manufacture and integration into a wireless communications terminal.
The present invention can provide integrated circuit transmit modules that include an integrated circuit substrate, a baseband I/Q modulator in the integrated circuit substrate that modulates an input signal to produce in-phase (I) and quadrature (Q) baseband modulated inputs, and a Built-In Self-Test (BIST) module in the integrated circuit substrate that monitors the I and Q baseband modulated outputs, to determine whether the baseband I/Q modulator is operating properly. By providing a BIST module in the integrated circuit substrate, operations of the baseband I/Q modulator can be monitored during manufacture and during subsequent field use. Autonomous testing of a baseband I/Q modulator thereby may be provided. In-circuit verification of output samples and feedback may be provided regarding the integrity of the output signal, for example to determine if the in-phase and quadrature baseband modulated outputs are corrupted due to excessive DC offsets and/or out-of-range digital signal processor samples.
According to embodiments of the present invention, a BIST module also generates test input data for the baseband I/Q modulator, such that the BIST module monitors the I and Q baseband modulated outputs in response to the test input data, to determine whether the baseband I/Q modulator is operating properly. According to other embodiments, the BIST module monitors the I and Q baseband modulated outputs in response to a communications input signal from a Digital Signal Processor (DSP), to determine whether the baseband I/Q modulator is operating properly.
Other embodiments of the present invention include a DSP interface module in the integrated circuit substrate that provides DSP data to the baseband I/Q modulator to be modulated. The BIST module provides the test input to the DSP interface module, such that the DSP interface module provides the test input data to the baseband I/Q modulator. Other embodiments also include a Central Processing Unit (CPU) or controller interface module in the integrated circuit substrate. The BIST module can generate a status signal to indicate whether the baseband I/Q modulator is operating properly. The status signal can comprise an analog and/or digital status signal and/or a multibit/multiword digital data communication. The CPU interface module is responsive to the status signal and can provide the status signal to a CPU.
According to other embodiments of the invention, a BIST module includes a first filter that is responsive to the input signal to produce a filtered input signal and a second filter that is responsive to the I and Q baseband modulated outputs, to produce a filtered output signal. A compare module compares the filtered input signal and the filtered output signal to determine whether the baseband I/Q modulator is operating properly. In other embodiments, the first and second filters are Finite Impulse Response (FIR) and/or Infinite Impulse Response (IIR) filters. The second filter models an analog filter that filters the I and Q baseband modulated outputs prior to providing these outputs to an RF modulator.
According to yet other embodiments, a BIST module further includes a phase and amplitude adjuster that is responsive to the first filter, to adjust the phase and amplitude of the filtered input signal, such that the compare module compares the filtered input signal having adjusted phase and amplitude, and the filtered output signal, to determine whether the baseband I/Q modulator is operating properly. According to still other embodiments, a compare module compares the filtered input signal and the filtered output signal, to determine whether a difference between the filtered input signal and the filtered output signal exceeds a tolerance value. The tolerance value may be fixed. Alternatively, in other embodiments, the CPU and/or other device provides the tolerance value to the compare module, for example via the CPU interface module.
Methods of testing integrated circuit baseband IQ modulators in an integrated circuit substrate according to embodiments of the invention monitor the I and Q baseband modulated outputs in the integrated circuit substrate and generate in the integrated circuit substrate an indicator of whether the baseband modulator is operating properly in response to the I and Q baseband modulated outputs that are monitored in the integrated circuit substrate. As was described above, test input data may be generated in the integrated circuit substrate for the baseband I/Q modulator. Alternatively, a communications input signal for the baseband I/Q modulator may be received in the integrated circuit substrate from a DSP and the I and Q baseband modulated outputs may be monitored in the integrated circuit substrate in response to the communications input signal to determine whether the baseband I/Q modulator is operating properly. FIR/IIR filtering, comparing and/or phase and/or amplitude adjusting may be provided, as was described above. A fixed or variable tolerance value may be used, as was described above. The indicator may comprise an analog and/or digital indicator and/or a multibit/multiword digital data indicator.
It will be understood by those having skill in the art that BIST systems and methods according to the invention may be used for integrated circuit baseband modulators and integrated circuit modulators other than baseband quadrature modulators. The BIST systems and/or methods may be integrated into a wireless communications terminal. Improved monitoring of modulator performance thereby may be provided, during and/or after production of the integrated circuit modulator, during and/or after manufacture of the wireless communications terminal that includes the modulator and/or during field operation of the wireless communications terminal.